I recently noticed that this weapon skill (as shown in the image) charges based on the player's use of the corresponding active skill, and it is not related to other player actions. Besides, interacting with witch stone will reset the accumulated charge.
Though I know that certain later talents can enhance the charging efficiency of this skill. However, this still results in players struggling to make use of this skill in the early stages of the game.
I hope that simple attacks or dealing damage could also contribute to a slight charge of this skill, or make the accumulated charge remain after resting.
This way, players can better utilize and familiarize themselves with this skill, gaining more experience to decide whether to enhance it with relevant talents.